1. Field of the Invention
The present invention relates to a substrate processing method and a substrate processing apparatus in which a substrate such as semiconductor wafer, liquid crystal display glass substrate, photo-mask glass substrate, optical disk substrate is rotated about a vertical axis in a horizontal plane, and the substrate is dried while feeding a cleaning solution such as de-ionized water onto the surface of the substrate.
2. Description of the Related Art
In a conventional process of manufacturing a semiconductor device, a circuit pattern is formed on a resist film of a substrate employing a lithography, for example, by the steps of applying a photo-resist on a silicone substrate, printing a circuit pattern onto a resist film on the substrate using an exposure device, and developing the resist film having been exposed with a developer. In the developing among these steps, the developer is fed onto the resist film having been exposed and formed on the surface of the substrate, for example, with the use of a slit nozzle, and thereafter, while the substrate is being rotated about the vertical axis in a horizontal plane, a cleaning solution (rinse) such as DI water is discharged on the center of the substrate from an outlet of the straight nozzle. The cleaning solution having been fed on the center of the substrate diffuses toward a circumferential edge of the substrate by a centrifugal force to spread all over the substrate, and washes out the developer from the resist film on the substrate surface. When this cleaning (rinsing) is ended, the feed of a cleaning solution from the nozzle onto the substrate is stopped, thereafter the number of revolutions of the substrate is further increased, and thus the cleaning solution on the resist film on the substrate surface is shaken off by the centrifugal force, whereby the substrate is dried (by spinning).
When the substrate is dried by spinning as mentioned above, however, a droplet of the cleaning solution may remain forming a spot on the substrate occurs. This is because, on the substrate having been processed, hydrophilic portions and hydrophobic portions coexist on the surface of the resist film, thereby leading to fluctuations in retention of the cleaning solution on the substrate. It is known that the droplet of the cleaning solution having remained as a spot on the resist pattern of the surface of the substrate like this is a factor of causing a development failure.
To overcome the above-mentioned problems, a method (so-called scan rinsing) has been proposed, and in which in the process of drying a substrate, while a cleaning solution is being discharged from an outlet of a cleaning solution discharge nozzle, the outlet of this discharge nozzle is scanned from the center of the substrate to the periphery thereof. In this method, since the drying goes on keeping a state that droplets of the cleaning solution are formed and held from the center of the substrate to the circumferential edge, the droplet of the cleaning solution is less likely to remain on the substrate, in spite of a resist film surface on which hydrophilic portions and hydrophobic portions are mixed. A further method has been proposed, and in which at the time of scanning a discharge nozzle of the cleaning solution while the cleaning solution is being discharged from the outlet of the discharge nozzle, with a gas blown out from an air jet nozzle, the air jet nozzle is moved from the center of the substrate toward the periphery together or in synchronization with the cleaning solution discharge nozzle (for example, refer to the Japanese Patent No. 3694641)
In the above-mentioned scan rinsing, as compared with a conventional spin drying, the development failure may be largely reduced. In the case, however, where the method of scan rinsing is applied to a substrate including a resist film surface of high water-repellent properties (for example, a contact angle of water is not less than 60°), it is found that the development failure occurs showing the following phenomenon.
That is, when the discharge nozzle is scanned from the center of the substrate toward the periphery while the cleaning solution is being discharged from the outlet of the cleaning solution discharge nozzle, first the entire surface of the substrate W is covered with a liquid film 3 of the cleaning solution, as illustrated in a plan view of the substrate of FIG. 7A, and subsequently the liquid film 3 in the center portion of the substrate W comes to be thinner to be brought in a state of just before being dried. Then, a portion 4 in the state of just before being dried indicated by a two-dot chain line (hereinafter, referred to as “portion just before being dried”), is spread outward by degrees as illustrated in FIG. 7B, and a dried core 5a is produced in the portion 4 just before being dried. This dried core 5a is enlarged to form a dried region 6a. This dried region 6a is spread all over the surface of the substrate W to dry the substrate W. However, in the case where the resist film surface on the substrate has high water-repellent properties, in the vicinity of the center of the substrate W, a second dried core 5b is produced following the production of the first dried core 5a within the portion 4 just before being dried, and there are some cases where a further new dried core is produced. Moreover, in the prior art, the discharge nozzle is merely moved from the center of the substrate W toward the periphery, so that a comparatively wide portion 4 just before being dried is formed in the vicinity of the center of the substrate W. Therefore, in the vicinity of the center of the substrate W, the second dried core 5b is produced in the portion 4 just before being dried, and sometimes a further new dried core is produced. Incidentally, no dried core is produced other than in the vicinity of the center of the substrate W. Then, as illustrated in FIG. 7C, the dried region 6a having been first formed is enlarged, and the second dried core 5b is enlarged to form a second dried region 6b, and this dried region 6b is enlarged as well.
The two dried regions 6a and 6b are enlarged respectively as mentioned above, and the two dried regions 6a and 6b are collided each other to be joined, as illustrated in FIG. 7D. Then, one dried region 6c is produced as illustrated in FIG. 7E. At this time, a droplet 7 of the cleaning solution is produced at a boundary portion between two dried regions 6a and 6b. Subsequently, although the dried region 6c that is formed by being joined into one is enlarged to the outside as illustrated in FIG. 7F, the droplet 7 of the cleaning solution remains as it is to the end. Then, although finally the entire surface of the substrate W will be dried as illustrated in FIG. 7G, the remaining droplet 7 of the cleaning solution will be dried as it is, and a dried mark (stain such as a water mark) 7′ of the cleaning solution remains as it is on the substrate W. As a result, a development failure will occur. Incidentally, the phenomenon as mentioned above is not limited to the case of drying by scan rinsing a substrate having been processed, but is found to happen generally in the case of a substrate having a surface of high water-repellent properties.
Additionally, according to the method described in the above-mentioned Japanese Patent No, 3694641, while an air jet nozzle that is disposed spaced apart by a predetermined distance from a cleaning solution (rinse) discharge nozzle is being moved from the center of the substrate to the periphery integrally or in synchronization with the cleaning solution discharge nozzle, a gas is blown out from the air jet nozzle, thereby the cleaning solution remaining on the substrate is dried and removed. By this method, however, the production of not less than two dried cores in the vicinity of the center of the substrate cannot be prevented. Moreover, when two dried cores are produced in the vicinity of the center of the substrate, even if the gas is blown to the substrate from the air jet nozzle, there is such occurrence as respective dried cores are enlarged ant thus the dried regions are spread, and then the two dried regions are collided each other to be joined into one. Consequently, a problem exists in that the production of dried marks of the cleaning solution that will be the cause of the development failure cannot be eliminated.